07 Columbia w. Acert oil pressure gauge not working right

The gauges on my 05 Columbia started doing similar things so I just replaced them and that seemed to fix it. However, my truck has the optional individual gauges.

I find that the needle moves around a fair bit at steady RPM but not as much as you describe, apparent this is because it it electronic and not mechanical.

 

If you have a scan gauge you can see what that says. If it gives a normal reading then then replace just the gauge. If it to is wacky replace the sending unit.

 

If it is an individual mechanical gauge, turning on the key wont change the gauge. If 25 is as low as it goes it is shot, replace it. If it is part of the electronic dash cluster then at best you have a bad ground, at worse the cluster is shot and needs replaced. If its electronic, a bad ground or bad cluster, usually all the gauges in the cluster start to act stupid at the same time. But if it is electronic, and oil pressure is the only one acting up I would start with the oil pressure sensor.